Method and apparatus for casting metal

ABSTRACT

Casting molten metal on a heated carrier liquid and solidifying metal while resting on carrier substance.

United States Patent Martin 1 Oct. 15, 1974 [54] METHOD AND APPARATUS FOR CASTING 1,831,310 11/1931 Lindemuth 164/81 METAL 2,363,695 11/1944 Ruppik 164/81 I 2,754,559 7/1956 Fromson 164/81 Inventor: Hubert Martin, Richmond, 3,430,680 3/1969 Leghorn 164/81 Assigns-e: Texce" Corporation Richmond Va. 3,508.599 4/1970 Vordahl 164/81 [22] Filed: Aug. 2, 1972 21 1 Appl' N0: 277,223 Primary Examiner-R. Spencer Annear Attorney, Agent, or FirmG. William King [52] US. Cl 164/81, 164/128, 164/337, 65/182 R [51] 1nt. Cl B22d 23/00 58 Field 61 Search 164/81, 128, 337; 264/298; [57] ABSTRACT 65/99 A, 182 R Casting molten metal on a heated carrier liquid and [56] References Cit d solidifying metal while resting on carrier substance.

UNITED STATES PATENTS 1,553,773 9/1925 Heal 65/182 R 3 Claims, 1 Drawing Figure METHOD AND APPARATUS FOR CASTING METAL This invention relates to a novel process for batch casting metal on a liquid carrier material for the purpose of producing castings with at least one flat, smooth surface in an economical manner. More specific ally, the present invention provides as its prime objective a process for producing metal articles having one or more smooth, planar surfaces, e. g, plates, strips, etc., all hereinafter generally referred to as smooth surface castings. The casting is carried out on a liquid carrier material of higher specific gravity than the metal to be cast and which is maintained at a temperature at least as high as the liquidus temperature of the cast metal. The invention is particularly suited for aluminum and its alloys, but is not limited thereto. As used herein, the term metal" is intended to mean a pure metal or any alloy combination which is to be cast. Casting of metal onto a carrier liquid is relatively new. The most pertinent prior art are two US. Pat. Nos. to Kuratomi, 3,565,154 and 3,587,710, which show processes, wherein a molten metal is dispersed on a liquid carrier such as lead maintained within a low temperature range.

Briefly, the present invention provides for the manufacture of castings having at least one very smooth surface in an economical manner. This is accomplished by initially maintaining the carrier liquid temperature during the actual casting no lower than the liquidus temperature of the cast metal, whereby the carrier liquid will not solidify any of the metal when contacted. This assures the cast metal the opportunity to spread quickly over the entire carrier liquid surface, provided sufficient metal is added and no physical flow obstructions are present. Thereafter, when the cast metal has reached a quiescent state while floating on the carrier liquid, a cooling is applied to the metal, either via the carrier liquid, or by cooling the top surface of the metal, or by a combination of these two methods to solidify the metal. The solidified metal is separated by conventional means from the carrier substance which may be still liquid or may be solid at this time.

The major distinguishing differences of the present invention from the Kuratomi patents are the utilization of the carrier liquid during casting at or above the liquidus temperature of the metal to be cast, the subsequent uniform spreading of the melt over the carrier liquid surface while the carrier liquid is still hot and the subsequent cooling and solidification of the melt.

Other objects and advantages of the invention will be seen by those skilled in this art from the following description of the best mode of carrying out the invention, and examples thereof, made in connection with the accompanying drawing, wherein:

The FIGURE is a vertical section view of the preferred apparatus for carrying out the process of the invention.

Referring to the drawing, the FlGURE illustrates the apparatus and the method by which a casting with at least one smooth surface is formed. The metal to be cast, or melt, is first heated to a molten state, cleaned, degassed in a well-known manner, and delivered into a feed vessel having outlet flow control means 25. The outlet 27 and inlet 29 may be positioned at different levels than shown with respect to casting 10; however, in its preferred form the invention contemplates use of a gravity feed underpour system as illustrated. The latter is designed to deliver the melt into the casting receptacle or mold 30 with little or no turbulence and the least amount of contamination to produce the highest quality casting possible.

A carrier liquid 40 of higher specific gravity than melt 15 is contained in mold 30. The liquid should have the following characteristics:

1. Its density in the operating temperature range must be higher than that of the metal to be cast.

2. It has to remain liquid without boiling in a temperature range from about 50 C above the metal liquidus temperature, preferably below the melt solidus temperature, but at least substantially below the liquidus temperature of the metal to be cast.

3. lt should be virtually inert to the melt to be cast, or capable of being separated from the melt by a third non-reactive material.

4. It should have a relatively low vapor pressure within the operating range.

There are several liquids which meet these requirements for aluminum and its alloys. Aluminum melts at 600 C. Most of its alloys solidify in a temperature range from slightly below 660 C to above 600 C.

For example, with aluminum as the melt to be cast, a good carrier liquid material is a ternary eutectic composed of 81.5 wt% BaCl 16.0 wt% KCl, and 2.5 wt% CaF with a eutectic temperature of about 560 C.

Another suitable group of heavy salts includes iodides and bromides. Lithium iodide, for instance, melts at 446 C, while a eutectic of 68 mole LiBr and 32 mole KBr forms a eutectic at about 320 C.

Still another group of carrier substances are the lowmelting heavy glasses. The system 3Pb'2SiO Na 0- 'SiO has one eutectic at 590 C with about 40 mole Pb0.

Finally, there are metals and their alloys as carrier liquids which form an immiscibility gap in the liquid with the metal to be cast as in the case of lead as carrier liquid and aluminum to be cast. While there is, at times, a slight solubility of the two metals in each other, as in the case of lead and aluminum, a metallurgical bond, and thus diffusion, can be readily avoided by protecting the heavy liquid surface with an adhering substance inert to both the carrier liquid and the metal to be cast.

the metal to be cast. If so desired, the air-filled space 65 above the carrier liquid is purged via means 60 with an inert gas, heated, if so desired, to the temperature above the liquidus temperature of the metal to be cast.

The desired amount of melt 15, controlled by device 25, enters via outlet 27 and inlet 29 into vessel 30, floats, due to its buoyancy through carrier liquid 40 and distributes itself evenly over the carrier liquid surface.

At the proper time the metal flow is terminated by closing outlet 27 with flow control device 25. The melt in vessel 30 is allowed to come to an equilibrium floating on the carrier liquid. The metal melt is then cooled and solidified by turning off all heating means, by cooling the carrier liquid 40 via heat exchangers 45 and, optionally, by introducing a cool gas via means 60 into space 65 on top of the metal.

After solidification is completed, lid 50 is removed from vessel 30 and the solidified casting is lifted from the carrier material and removed from vessel 30. The apparatus is then prepared for the next casting cycle.

The horizontal cross-sectional shape is determined by the desired perimetral shape of the casting. It is, however, within the scope of this invention to place inert separators and indentors into the melt from the vessel floor or from above so that more than one casting can be made at a time as well as castings with shaped surfaces. The process, therefore, has a large degree of freedom as to the number of castings made at a time, their shapes, their surface configurations and their thicknesses. Marinite and glassrock are suitable inert materials for this purpose.

In another modification of the invention the side walls of vessel 30 may be provided with an electromagnetic field of sufficient strength to repel the melt in order to prevent meltwall contact and thus binding of melt to the wall. Similarly, the separators and indentors mentioned in the previous paragraph may also be equipped with electrical means to provide an electromagnetic field of sufficient strength to repel the melt from their surfaces.

In still another modification of the invention preferential cooling and solidification of the casting(s) may be effected, e.g., by cooling first the center section of a casting to obtain a particularly desirable preferred orientation of the grain structure in the solidified casting or to control shrinkage problems due to volume changes during solidification.

It is also within the scope of this invention to protect the upper metal surface before, during, and after solidification from oxidation. This can be accomplished by either a third liquid layer having similar characteristics as the carrier liquid but a specific gravity lighter than that of the metal to be cast, or by an inert gas.

It is also within the scope of this invention to apply a medium between the metal and the carrier liquid which prevents diffusion of one into the other and facilitates separation after solidification of the casting or after solidification of both casting and carrier material.

EXAMPLE I To produce an aluminum casting, use a carrier liquid having the following approximate composition:

81.5 weight BaCl -61 mole percent) 16.0 weight KCl (-34 mole percent) 2-5 weight CaF (-5 mole percent) Such a mix forms a ternary eutectic at about 560 C and has a density higher than liquid or solid aluminum. lts vapor pressure is low and it does not react with aluminum.

The metal cast is alloy 356, a typical aluminum casting alloy, with a composition (in weight percent) of:

Remainder trace elements Such an alloy is fully solidified at 580C. C/

Prepare the aluminum alloy by melting, cleaning, degassing by conventional means and charge the feed vessel.

Prepare vessel 30 by melting the salt mix of the above composition and raising its temperature to 660 C. While heating and after putting lid 50 onto vessel 30, purge the air from the space above the carrier liquid with nitrogen. lntroduce alloy 356 at 665 '2 5 C, via the flow control, the outlet 27 and inlet 29, into vessel 30 until the desired metal thickness is reached in vessel 30, the alloy spread and floating on top of the carrier liquid. With no more metal entering vessel 30 the metal layer reaches quickly a quiescent state with a plane interface between metal and carrier liquid.

Turn off all heating systems and activate the cooling systems but maintain the carrier liquid barely above its solidification temperature of 560 C. Thus the metal solidifies quickly in situ.

Remove lid 50 from vessel 30 and subsequently the alloy casting from vessel 30 by conventional means.

EXAMPLE ll This example follows the same procedure as Example I except the carrier liquid is cooled to below its solidus temperature, adheres to the alloy casting when the latter is removed from vessel 30 and is, later, mechanically removed from the casting.

EXAMPLE 1]] This example follows the same procedure as in Example l with the following exceptions:

The carrier liquid is lead alloyed with 0.2 percent (wt) aluminum (saturation at 658 C). A protective agent adhering to the lead surface in vessel 30 is added to prevent diffusion of lead into aluminum and to facilitate separation of the solidified casting from the lead. The aluminum if introduced into vessel 30 not by underpouring but by gently pouring it onto the lead surface. The lead in vessel 30 is initially at a temperature of 660 i 5 C and cooled at the proper time to below 500 C.

Aluminum and its alloys are most suitable for this casting process, however, other metals and their alloys, including magnesium, beryllium, and even iron and steel may also be processed by this technique, provided the well known protective measures are taken to prevent oxidation and health hazards and provided the proper heavy carrier liquids are selected.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments, are therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claim or, therefore, intended to be embraced therein.

-What is claimed and desired to be secured by United States Letters Patents is:

1. Apparatus for casting metal material comprising a feed vessel having a controlled outlet, a virtually closed mold vessel adapted to contain a carrier liquid on which said metal material is to be cast, an inlet in said mold vessel positioned to receive said metal material from said feed vessel and deliver the same into said mold at below the normal surface level of said carrier liquid, and one or more separators or indentors positioned in said mold vessel to permit one or more castings of said metal material at one time with varied surface configurations, if desired.

2. A method of batch casting a metal material into an article having a smooth, flat surface comprising the steps of melting said metal material, melting a carrier material of higher specific gravity than said metal material and maintaining the temperature of said carrier material in a stationary mold at a temperature equal to or above the liquidus temperature of said metal material to form a smooth, flat, liquid mold surface, and dispersing the molten metal material to be cast onto said fiat liquid top surface of said carrier material while at or above the liquids, temperature of said metal material, said metal material being dispersed on said carrier liquid by introducing said metal material below the surface of said carrier liquid and causing said metal material to float upwardly onto the surface of said carrier liquid in a smooth, even manner to form a casting layer thereon, and thereafter cooling said metal material in situ in said mold.

3. A method as defined in claim 2 wherein said lower specific gravity substance is an inert gas maintained at a temperature at least as high as the liquidus temperature of said metal material at least during the time said metal is introduced into said mold. 

1. Apparatus for casting metal material comprising a feed vessel having a controlled outlet, a virtually closed mold vessel adapted to contain a carrier liquid on which said metal material is to be cast, an inlet in said mold vessel positioned to receive said metal material from said feed vessel and deliver the same into said mold at below the normal surface level of said carrier liquid, and one or more separators or indentors positioned in said mold vessel to permit one or more castings of said metal material at one time with varied surface configurations, if desired.
 2. A method of batch casting a metal material into an article having a smooth, flat surface comprising the steps of melting said metal material, melting a carrier material of higher specific gravity than said metal material and maintaining the temperature of said carrier material in a stationary mold at a temperature equal to or above the liquidus temperature of said metal material to form a smooth, flat, liquid mold surface, and dispersing the molten metal material to be cast onto said flat liquid top surface of said carrier material while at or above the liquids, temperature of said metal material, said metal material being dispersed on said carrier liquid by introducing said metal material below the surface of said carrier liquid and causing said metal material to float upwardly onto the surface of said carrier liquid in a smooth, even manner to form a casting layer thereon, and thereafter cooling said metal material in situ in said mold.
 3. A method as defined in claim 2 wherein said lower specific gravity substance is an inert gas maintained at a temperature at least as high as the liquidus temperature of said metal material at least during the time said metal is introduced into said mold. 